Tammy is a member of an electric utility cooperative. As a member, she pays monthly for the electricity she uses, but if the utility has a net profit for the year, she will receive a rebate. In 2017 she paid $3,600 for her utilities and because the cooperative had a profit for 2017, in 2018 she received a check for $360. Why would the tax treatment of the rebate differ if the utilities were used in Tammy's business as compared to her personal residence?